This invention is concerned with the design and manufacture of paint can bottoms. Paint cans are over 61/2" in diameter for the popular one gallon size and the can body is made from a flat blank of sheet metal rolled into a cylinder and joined along the meeting longitudinal edge. This rolled cylindrical body is conventional throughout the industry and is manufactured from tinplate. To the body is doubleseamed a circular bottom closure and a top ring designed to receive the top closure or plug.
The present disclosure is concerned with the design and manufacture of a bottom end closure which has greater resistance to creasing and fracturing from fatique stress. The standard size 610.times.703 height diameter one gallon paint can is filled with 10 to 13 pounds of paint and tends to be abused in normal packing and shipping. The can makers convention gives the diameter across the completed doubleseam in inches plus sixteenths of an inch then the height in inches plus sixteenths of an inch. Therefore, the foregoing container is 6 10/16" in diameter by 7 8/16" in height.
More particularly, if a paint container is dropped and/or bumped, it is expected that the bottom end closure will suffer the greatest deformation. The bottom end closure buckles or creases radially across the transition between the various areas of the profile. These transitions are usually circular and concentrically located and consist of little more than a series of radii representing and defining re-enforced areas which act to prevent the bottom from flexing or warping. It should be appreciated that paint cans suffer greater stresses than other cans of similar design because of their larger size and the heavier weight of the contents in them. One easy solution to overcoming dynamic and static loadings is to increase the thickness of material from which the container bottom end closure is made. That is an unacceptable approach in that more material, more energy and more cost for manufacture and shipping are incurred with that solution. Another approach which has some potential for minimizing the thickness of the container bottom end closure would be to use higher strength materials and maintain the lighter gauge. This solution is normally unacceptable in and of itself because higher strength materials tend to have less fatique resistance because of their minimal ductility.
It has been found that the balance between maximum static strength and dynamic strength resides in the overall configuration of profile applied to the bottom. This configuration or profile is critical to achieving an overall efficient combination of plate weight, plate type and dynamic and static strength.